Air cooled turbine wheel design



Dec. 23, 1958 M. MOSESON 2,865,598

AIR COOLED TURBINE WHEEL DESIGN Filed March 3, 1954 INVENTOR MERLA/VD L.MOSESO/V ATTORNEYS AIR COQLED TURBTNE WHEEL DESIGN Merland L. Moseson,Berea, Ohio, assignor to the'United States of America as represented bythe Secretary of the Navy Application March 3, 1954, Serial No. 413,977

7 Claims. (Cl. 253-3915) (Granted under Title 35, U. S. Code (1952),sec. 266) This invention relates to an integral turbine blade andturbine wheel construction for utilization in applications where lightweight is required and where blade replacement is not a factor to beconsidered.

In prior art turbine wheel constructions, the turbine blades are fcrgedor cast with an integral blade base or root which forms a platform forthe airfoil portion of the blade. The blade base is then broached ormachined to form a fir tree, dovetail, or other type of mechanicalfastening for attachment to the turbine disk. The turbine disk is forgedand a rim forging composed of a heat resisting alloy is welded to thehub portion of the disk. This rim forging of heat resisting alloy isthen machined to provide blade fastening slots therein into which thebases of the turbine blades are fitted and suitably at tached. The diskand rim forgings are heavy and costly to produce and have the furtherdisadvantage that the interruptions in the outer portion of the rim,into which the blade bases are fitted, causes a great portion of the rimto become a dead load, that is, this outer portion of the rim addsweight to the turbine wheel without providing a corresponding amount ofstrength to the turbine wheel. Furthermore, the blade bases areobjectionable in the same respect because they dictate the use of Widerims on the turbine disks to bring the bearing and shear stresses in thefastening within acceptable limits. The only essen- '[iPl part of therim load cm a turbine disk is caused by the airfoil portions of theturbine biades. Thus, in turbine wheels of conventional design all ofthe centrifugal load, during operation, which is caused by the blades,blade bases, and the interrupted portion of the rim must be transierredto the disk at the maximum diameter of the uninterrupted portion of thedisk. Some of the prior art has proposed the use of hollow, air cooledturbine blades to reduce the weight of the turbine wheel. However, thebasic limitations of the interrupted wheel rim and the conventionalmodes of attaching the blade roots to the wheel rim still exist in theprior art constructions in spite of the weight reduction due to thehollow blades. These factors account for most of the load on the turbinewheel. It is to be further noted in connection with the prior artconstructions mentioned above that there are a relatively small numberof industrial installations which are capable of making turbine wheelconstructions as taught by the prior art.

The present invention proposes to overcome the drawbacks of the priorart by disclosing an integral turbine blade and turbine wheelconstruction for utilization in applications where light weight isrequired and where blade replacement is not a factor to be considered.Broadly, the present invention consists of a plurality of light weightair cooled blades having interior heat transfer surfaces formed bycorrugations separating the blades from island shaped inserts. Theblades are extended down between, and attached to, two light weightcircular disks, which form the hub portion of the turbine wheel. Ashroud is further provided which fits between the wheel disks and aroundthe turbine blades at the periphery of the disks 2,8558 Patented Dec. 231958 lCQ for the purpose of sealing the voids at the periphery of thewheel. This particular construction permits weight reduction at the rimof the disk by precluding the need for any interruption of the diskrims. In operation the centrifugal load of theblade is transferredgradually to the disks and this construction provides the furtheradvantage of carrying a portion of the load to the cooler regions of thedisk where permissible disk stress levels are higher. The abovementioned island shaped inserts are attached to the disk rims in such amanner as to carry their own loads and part of the load of the abovementioned corrugations to the disks rather than first transferring thisload to the above mentioned outer shroud which is one of V the hottestmembers of the assembly. The turbine wheel assembly is provided withcooling air which is fed between the disks through a hollow shaft uponwhich the assembly is mounted. This cooling air passes radially from theassembly through the above mentioned corrugations and discharges out ofthe tips of the blades into the main gas. stream of the turbine.

it is accordingly one object of this invention to disclose a turbinewheel which is much lighter than any known design of equivalent tipdiameter or capacity.

it is a further object of this invention to disclose a turbine wheelwherein the centrifugal load from a set of blades is graduallytransmitted to the disk portion of the wheel at various radial positionson the wheel disks without interrupting the rim circumference of thedisks. In this manner some of the load is transmitted to cooler centralportions of the disks where higher stresses are permitted.

It is another object of this invention to obviate the necessity ofhaving thick turbine disk rims to acconnno date the shear and bearingstresses of conventional blade fastenings.

it is'a further object of thisinvention to disclose an air cooledturbine wheel wherein the blade bases, or skirts, serve as both impellervanes and stiffening ribs for the wheel disks.

it is another object of the instant invention to disclose an air cooledturbine wheel construction wherein an insert placed within the bladerestricts theflow of cooling air to regions near the inner surface ofthe blade shell and thereby requires a minimum of cooling air and makesthe most effective use of the cooling air thus required.

It is another object 'of this invention to disclose a turbine wheelconstruction which can be fabricated out of ferritic steels instead ofthe high heat resisting alloys which are presently used. The ferriticsteels can be used because of the more efficient cooling of the turbinewheel assembly.

It is another object of this invention to disclose a turbine wheelconstruction which can be fabricated by the use of conventional machinetools and sheet metal techniques and therefore does not require thespecialized machinery and expert skill which is presently required.

It is another object of the invention to disclose a turbine wheelconstruction which readily lends itself toward the conservation ofmaterials in its manufacture both by requiring a lesser weight ofmaterial for its construction and by decreasing the amount of materials7 assembly;

Fig. 3 is a cut-away view showing the island portion of the blade'having corrugations surrounding it;

Fig. 4 is a view, partially cut-away, which shows the outer blade shellof the blade assembly mounted on the island insert and on the corrugatedportions of the blade integral therewith, are arms 11 and 12 to whichare suitably attached or affixed tabs 13 and 14. Tabs 13 and 14 areadapted to be welded, brazed, or otherwise suitably secured to theperipheral flared rim portions 15 and 16 of wheel disks 17 and 18,respectively, Fig. 1. The

wheel disks 17 and 18, in their most rudimentary form consist of lightweight circular plates, having circular apertures (not numbered)centrally located therein. These apertures serve to mount disks 17 and18 upon hollow shaft 19. However the disks 17 and 18 shown in Fig. 1have flared portions 15 and 16. This construction allows the use ofturbine blades having narrow root portions and wider airfoil bladeportions. It can be readily seen that in fabricating the turbine wheel aplurality of island inserts are to be positioned and affixedcircumferentially about the peripheries of plates 17 and 18. Thefollowing description will refer to the only one turbine blade assemblydesignated by numeral 20, Fig. 5,

but it is to be understood that in the fabrication of a turbine wheelunit a plurality of these assemblies are to be afixed to the disks 17and 18.

An outer blade shell generally designated by numeral 21 is adapted tofit over and partially surround island insert 10. Blade shell 21consists of an airfoil portion 22 and a hollow elongated skirt 23, Fig.4, effectively formed integrally with airfoil portion 22. Positioned atthe base at both ends of airfoil section 22 are flanges 24 which areadapted to seat on the insert tabs 13 and 14, Fig. 4. The position offlanges 24 on airfoil section 22 determines the relative radialpositioning of the wheel disks 17 and 18 and blade shells 21. The edges25 and 26 of hollow elongated skirt 23 of blade shell 21 are adapted tobe welded, brazed, or otherwise suitably affixed to wheel disks 17 and18. It can thus be seen that this type of blade construction obviatesthe necessity for interruption of the disk rims. Furthermore since theheat, during turbine operation, is much greater at the rim portions and16 than at the more centrally located portions of disks 17 and 18, itcan be seen that this construction is advantageous since the centrifugalstress of the turbine blade is distributed radially along the disks 17and 18 rather than being concentrated at the hotter outer portions ofthe turbine disks which are weaker than the more centrally locatedcooler portions. Since the tabs 13 and 14 of the island insert 10 areaffixed to the rims of disks 17 and 18, they carry their own load and donot depend on the connections between the outer blade shell 21 and thedisks 17 and 18 for support.

The elongated skirt portion 23 of the turbine blade shell 21, inaddition to serving the function of aifixing the blade shell 21 tothewheel disks 17 and 18, also serves the function of providing a series ofrigid connections between wheel disks 17 and 18. These rigid connectionsact as ribs to unite the wheel disks 17 and 18 and the blade assemblyinto a strong unitary turbine wheel structure. The radially extendingskirt portion 23 serve the further function of acting as impeller vanesfor the cooling air as will be more fully described hereafter.

Reference is now made to Figs. 3, 4 and 5. A corrugated intermediatestructure 27 is adapted to be positioned between island insert 10 andthe blade airfoil portion 22. This corrugated structure 27 providesbracing between island insert 10 and the blade airfoil portion 22, andis attached between the latter two members as by welding or brazing, orin any other suitable manner. It will be noted at this point that thestructure of the corrugations provides air ducts through which coolingair flows.

Cooling air is supplied to the turbine blade assemblies from a suitablecompressor (not shown) via hollow shaft 19 as shown by the arrows inFig. 1. Shaft 19 has a conical portion 28 having apertures 29 in itsperiphery through which the cooling air flows. Portion 28 of the shaft19 is conical in order to provide adequate circumferential space for theflow of air in addition to providing increased rigidity to thestructure. A conically shaped sealing plug 30 is afiixed to the insideof the conical portion 28 of shaft 19, Fig. l. The plug 30 has thefunction of directing the flow of cooling air to apertures 29 inaddition to the functions of sealing the end of shaft 19 and providinggreater rigidity for shaft 19. As the cooling air passes radiallyoutward from apertures 29 it is given tangential velocity by the skirtextension 31 Figs. 4 and 5 which acts as an impeller vane. The skirtextension 31, it will be noted, is provided only on one side of skirt23, namely, on the suction side thereof. This is for the purpose ofgenerating radial flow of the cooling air prior to the entry of thecooling air into the compartment formed by the walls of hollow skirt 23.It can thus be seen that the cooling air flows through hollow skirt 23.However since the island insert 10 is sealed against the entry of air,the cooling air is forced around insert was shown by the arrows in Fig.2

and through the ducts formed by corrug1tions'27. It can thus be seen thecooling air is forced between the outside of island insert 10 and theinside of the blade airfoil portion 22. In this manner a minimum ofcooling air is required and that which is required is kept in the mosteffective location, namely, in contact with the blade shell airfoilsection 22. The cooling air after passing radially through the coolingducts formed by the corrugations 27 in the blade assembly 21 dischargesout of the tip of the blades into the gas stream of the turbine.

A sealing shroud 32, Figs. 1 and 5, fits around the blade shell airfoilportion 22 and has its edges suitably attached to the flared rims 15 and16 of wheel disks 17 and 18, respectively. Lips 33 of shroud 32 fitsnugly or may be welded or brazed to blade airfoil section 22. Thesealing shroud 32 serves the function of sealing the turbine wheelassembly so that the cooling air is forced through its aforementionedpath in contact with the inner surfaces of blade airfoil section 22. Inaddition to this function it also serves to lend greater rigidity to theturbine wheel assembly. The sealing shroud 32 may consist of anindividual segment, Fig. 5, for each blade assembly or may be made ofsegments which are large enough to accommodate a plurality of bladeassemblies. A portion of the cooling air may circulate by convectionwithin the space defined by the wheel disks 17 and 13, the skirtportions 23, and the sealing shroud 32. Alter nately, bleed apertures 34may be provided in the shroud 32 for allowing partial bleed of thecooling air. The choice of either of the foregoing constructions dependson the cooling requirements needed for the particular application underconsideration.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefcre to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

Having thus described my invention I claim:

1. A turbine wheel assembly comprising a hollow shaft, a pair of spaceddisks mounted on said shaft, communicating apertures in said shaftleading from said hollow portion of said shaft to the space between saidspaced disks, a plurality of turbine blade assemblies radially mountedin circumferentially spaced relationship between said disks, each ofsaid assemblies consisting of an island insert, said island insert beingaffixed to the peripheral portions of said disks, a hollow blade shellhaving an airfoil portion and a skirt portion, said airfoil portionsurrounding said island insert along the longitudinal axis thereof, saidskirt portion extending radially between said spaced disks and beingaffixed to each of said spaced disks, a corrugated intermediate memberpositioned between said island insert and said blade airfoil portion,and a sealing shroud extending between said disk peripheries and aroundsaid blade assemblies substantially at the junction of said airfoil andskirt portions of said blade shell.

2. A turbine wheel assembly comprising a hollow shaft, a plurality ofspaced disks mounted on said shaft, said disks being free of undercutsand transverse cutouts adjacent the peripheries thereof, communicatingapertures in said shaft positioned between said spaced disks, aplurality of turbine blade assemblies extending in a sub stantiallyradial direction with respect to said disks and being circumferentiallyspaced with respect to said disks, said turbine blade assembliesconsisting of a hollow turbine blade shell having an airfoil portion anda skirt portion, said airfoil portion extending beyond the peripheriesof said disks, said skirt portion being elongated and extending betweensaid disks and having one side thereof affixed to each of said disksover a region extending radially inwardly of the disk rim, and a sealingshroud extending between said disk peripheries and around said bladeshell substantially at the junction of said airfoil and skirt portionsof said blade shell.

3. A light weight turbine wheel assembly adapted to be air cooledcomprising a hollow shaft for conducting cooling air, a plurality ofspaced disks mounted on said shaft, communicating apertures in saidshaft positioned between said disks to conduct cooling air from saidhollow shaft to the space between said disks, a plurality of turbineblade assemblies circumferentially positioned with respect to said disksand extending substantially radially with respect to said disks, each ofsaid assemblies comprising an island insert affixed to the peripheralportions of said disks, a hollow blade shell having an airfoil portionand an elongated skirt portion, said airfoil portion extending aroundsaid island insert in a longitudinal direction, said elongated skirtportion extending between said disks and being affixed thereto, anintermediate member positioned between said island insert and said bladeairfoil portion for supporting the latter two members relative to eachother, and a sealing shroud extending between said disks and around saidblade shells for sealing the turbine wheel assembly whereby the coolingair is caused to flow from the space between the disks through the skirtportion of the blade shells and then between the island insert and theinterior surface of the airfoil portion for the purpose of cooling theairfoil portion of said blade assembly.

4. A light weight turbine wheel assembly adapted to be air cooledcomprising a pair of spaced disks having uninterrupted peripheries, aflared rim portion on each aseaees of said disks, said flared rimportion on each of said disks extending away from the other of saiddisks, a plurality of turbine blade assemblies mounted incircumferentially spaced relationship about said disks and extendingsubstantially radially with respect to said disks, each of said bladeassemblies comprising an island insert affixed to said disk rims, ahollow turbine blade having an airfoil portion and a skirt portion whichis narrower than said airfoil portion, said airfoil portion surroundingsaid island insert in a longitudinal direction and extending beyond saiddisk rims, said skirt portion extending between said disks and beingaflixed to each of said disks, ribbed members afiixed between saidisland insert and said blade airfoil portions, and a sealing shroudaffixed to each of said runs.

'5. A turbine wheel assembly adapted to be air cooled comprising a pairof spaced circular disks, a plurality of turbine blade assembliesmounted in circumferentially spaced relationship relative to said disks,said assemblies comprising an island insert affixed to the peripheralportions of said disks, a turbine blade shell having an airfoil portionand an elongated skirt portion, said airfoil portion surrounding saidisland insert in a longitudinal direction, said skirt portion extendingbetween said disks and being aflixed to each of said disks, anintermediate bracing structure afiixed between said island insert andsaid turbine blade airfoil portion, and a sealing shroud affixed betweenthe peripheral portions of said disks, said sealing shroud having bleedapertures therein.

6. A turbine wheel assembly as set forth in' claim 5 wherein a skirtextension is affixed to one side of said elongated blade skirt.

7. A light weight turbine wheel assembly adapted to be air cooledcomprising a plurality of spaced disks having uninterrupted rimportions, a plurality of turbine blade assemblies mounted incircumferentially spaced relationship relative to said disks, each ofsaid assemblies comprising an island insert affixed to said rimportions, a turbine blade shell having an airfoil portion and a skirtportion which is narrower than said airfoil portion, said airfoilportion surrounding said island insert in a longitudinal direction, anintermediate structure aflixed between said island insert and saidairfoil portion, said skirt portion extending between said disks andbeing affixed to each of said disks, a blade skirt extension attached toone side of said elongated skirt portion, and a sealing shroud affixedbetween the peripheral portions of said disks.

References Cited in the file of this patent UNITED STATES PATENTS

